Process for the preparation of low branch content polybutadiene

Abstract

A process for the preparation of low branch content polybutadiene comprising: (a) a first butadiene polymerisation stage; (b) treatment of the polymer solution obtained upon completion of stage (a) with a coupling agent selected from: (i) polyunsaturated natural oils; (ii) butadiene and/or isoprene oligomers; (iii) butadiene and/or isoprene co-polymers with vinylarene monomers; the unsaturations present in compounds (i)–(iii) being at least partially substituted with groups selected from epoxides, anhydrides and esters; (c) recovery of the low branch content polybutadiene obtained upon completion of stage (b).

1. A process for the preparation of low branch content polybutadiene having the following characteristics:
 a branch index value (g M ) of less than 1; 
 a damping coefficient (tan δ) value, defined as the trigonometric tangent of the ratio between the viscous modulus (G″) and the elastic modulus (G′) [tan δ=G″/G′] measured at 0.01 Hz, 100° C. and 1% strain, from 0.80 to 1.40; 
 a Mooney viscosity of less than 49; 
 M w /M n  less than 2.5; 
 a 1,4-cis unit percentage greater than 93%; 
 the aforementioned process comprising the following stages: 
 (a) polymerisation of the butadiene in the presence of organic solvents and in the presence of a catalytic system comprising (a1) a neodymium derivative selected from neodymium carboxylates, the aforesaid neodymium carboxylates being devoid of water and —COOH groups; (a2) an aluminium alkyl of general formula (Ia) AlR 4   3  or (Ib) AlH n R 4   3−n  wherein “n” is from 1 to 2 and R 4 , being either identical or differing from one another, represent an alkyl radical containing from 1 to 10 carbon atoms; (a3) an organo-aluminium derivative containing at least one halogen atom; 
 the aforesaid first stage giving rise to a linear polybutadiene (g M =1) with a 1,4-cis unit content greater than 93%, and a M w /M n  ratio of less than 2.5; 
 (b) treatment of the polymer solution obtained upon completion of stage (a) with a coupling agent, thus obtaining low branch content polybutadiene having the above mentioned characteristics; 
 (c) recovery of the low branch content polybutadiene obtained upon completion of stage (b); the aforementioned process being characterised in that the coupling agent is selected from: 
 (i) unsaturated natural oils; 
 (ii) butadiene and/or isoprene oligomers; 
 (iii) butadiene and/or isoprene copolymers with vinylarene monomers; 
 the unsaturations present in compounds (i)–(iii) being at least partially substituted with groups selected from epoxides, anhydrides and esters. 
 
     
     
       2. The process according to  claim 1 , wherein the low branch content polybutadiene has a branch index (g M ) of from 0.92 to 0.99. 
     
     
       3. The process according to  claim 2 , wherein the low branch content polybutadiene has a branch index (g M ) of from 0.93 to 0.97. 
     
     
       4. The process according to  claim 1 , wherein the low branch content polybutadiene has a damping coefficient (tan δ) value of from 0.90 to 1.30. 
     
     
       5. The process according to  claim 1 , wherein the low branch content polybutadiene has a Mooney viscosity of from 35 to 48, M w /M n  of from 2.0 to 2.4 and a 1,4-cis unit percentage greater than 94%. 
     
     
       6. The process according to  claim 5 , wherein the low branch content polybutadiene has a Mooney viscosity of from 35 to 46, M w /M n  of from 2.1 to 2.2 and a 1,4-cis unit percentage greater than 95%. 
     
     
       7. The process according to  claim 1 , wherein during stage (a) a linear polybutadiene having a M w /M n  value of from 2.0 to 2.4 is obtained. 
     
     
       8. The process according to  claim 7 , wherein the M w /M n  value ranges from 2.1 to 2.2. 
     
     
       9. The process according to  claim 1 , wherein the neodymium carboxylates used in stage (a) are selected from the group consisting of neodymium versatate, neodymium pivalate, neodymium 2-ethyl-hexanoate, and mixtures thereof. 
     
     
       10. The process according to  claim 1 , wherein the temperature of stage (a) varies from 20 to 120° C. 
     
     
       11. The process according to  claim 1 , wherein during stage (a), the ratio between the (a1) and (a2) components ranges from 1/0.5 to 1/30. 
     
     
       12. The process according to  claim 1 , wherein during stage (a), the ratio between the (a1) and (a3) components ranges from 1/0.5 to 1/10. 
     
     
       13. The process according to  claim 1 , wherein during stage (a) the (a1) component is added to the reagent mixture as the final ingredient. 
     
     
       14. The process according to  claim 1 , wherein the temperature during stage (b) varies from 20 to 150° C. 
     
     
       15. The process according to  claim 14 , wherein the temperature during stage (b) varies from 70° C. to 120° C. 
     
     
       16. The process according to  claim 1 , wherein the coupling agent is selected from the group consisting of epoxidised seed oils, epoxidised polybutadienes, maleinised polybutadienes, epoxidised styrene-diene co-polymers, maleinised styrene-diene co-polymers, and mixtures thereof. 
     
     
       17. The process according to  claim 1 , wherein compounds (i)–(iii) comprise at least 1.5 functional groups per molecule. 
     
     
       18. The process according to  claim 17 , wherein compounds (i)–(iii) comprise from 3 to 6 functional groups per molecule. 
     
     
       19. The process according to  claim 1 , wherein the coupling agent used during stage (b) is present in quantities ranging from 0.1 to 0.6 equivalents, with respect to the number of polymer chains present in the system. 
     
     
       20. The process according to  claim 19 , wherein the coupling agent used during stage (b) is present in quantities ranging from 0.2 to 0.4 equivalents, with respect to the number of polymer chains present in the system. 
     
     
       21. Sulphur-vulcanisable elastomeric mixtures comprising an elastomeric component comprising at least one polybutadiene having a 1,4-cis unit level greater than 93%; the aforementioned at least one polybutadiene comprising the following properties:
 a) a polydispersity index of from 2.0 to 2.3; 
 b) a tan δ value of from 0.8 to 1.40; 
 c) a g M  value of between 0.92 and 0.99; 
 d) a Mooney viscosity value of from 35 to 48. 
 
     
     
       22. The sulphur-vulcanisable elastomeric mixtures according to  claim 21 , wherein the at least one polybutadiene comprises the following properties:
 a) a polydispersity index of from 2.1 to 2.2; 
 b) a tan δ value of from 0.90 to 1.30; 
 c) a gm value of from 0.93 to 0.97; 
 d) a Mooney viscosity value of from 39 to 46. 
 
     
     
       23. The sulphur-vulcanisable elastomeric mixtures according to  claim 21 , further comprising carbon black in quantities of from 20 to 350 parts per 100 parts of the elastomeric component.